1. Field of the Invention
This invention relates to an apparatus for electrically driving a retractable antenna installed in vehicles such as automobiles, more particularly to an electrically driving apparatus for protruding and retracting (elevating and lowering) a retractable antenna by longitudinally transferring a rod antenna element of the antenna directly by means of a feed roller.
2. Description of the Related Art Japanese Patent Application KOKAI Publication No. 59-27604, for example, discloses an apparatus for electrically driving a retractable antenna. This apparatus comprises a worm wheel engaged with a worm gear coupled with a motor, a first grooved roller arranged coaxial with the worm wheel, and second and third grooved rollers which are arranged at the positions obliquely opposed to the first roller by urging means such as a spring. The first through third roller are urged against the outer periphery of a rod antenna element by the urging means. The first through third roller can be rotated by the rotational force of the motor, so that the rod antenna element is longitudinally transferred. Thus, the antenna is protruded and retracted (elevated and lowered).
This antenna driving apparatus, however, has the defect that the urging force of the urging means such as a spring is hard to be transmitted as an effective transfer force to the outer periphery of the rod antenna element. Therefore, if water, oil, etc. is adhered to the outer periphery of the rod antenna element, a slip may occur between the rollers and the rod antenna element, which makes it difficult, for example, to reliably transfer the rod antenna element.
In the above-described conventional retractable antenna electrically driving apparatus, a slip may easily occur between the rollers and the rod antenna element, and hence the rod antenna element is hard to transfer in a reliable manner. In light of this, the apparatus is not considered so practical.